This invention relates to pressure transducers and particularly to pressure transducers capable of measuring extremely high pressures.
As is well known, pressure transducers generally employ piezoresistive elements, which are disposed on a silicon sensor and which when subject to a force or pressure, exhibit a change in resistance. Such devices have been used with oil, which oil or fluid is employed as a force transmitting medium. In certain applications, the external pressure applied to a diaphragm or transducer can be very large. These devices frequently employ a metal diaphragm as a force collector and a media isolator. The metal diaphragm communicates with a silicon pressure sensor through an oil filled reservoir, which is contained in an internal hollow in the transducer housing. For examples of such prior art devices, reference is made to U.S. Pat. No. 4,406,993, entitled, xe2x80x9cOil Filled Pressure Transducers,xe2x80x9d issued on Sep. 27, 1983, to Anthony D. Kurtz, the inventor herein, and assigned to Kulite Semiconductor Products, Inc., the assignee herein.
Such pressure transducers have been used in very hostile environments, such as in combustion or diesel engines where the temperatures and pressures can be extremely high. As one knows, the metal isolation diaphragm must be fairly compliant to deflect and to accommodate the increase in oil volume. In these devices the large induced pressure would build up in the oil, which will be transmitted to the silicon sensor. Such devices have operated at pressures of 30,000 psi or greater.
When attempting to operate such transducers at extremely high pressures, such as pressures which approach 75,000 psi or greater, one experiences severe problems in transducer operation. The transducers, when subjected to such huge pressures, experience the rupture of terminal pins which are associated with the header. These pins or contacts are actually pushed out. The transducer cannot hold the oil because the header ruptures due to such large pressure. This becomes a serious problem. Thus, the use of pressure transducers at pressures which are on the order of magnitude of 75,000 psi or higher is extremely questionable, and such devices are subjected to extreme problems, which can render the devices unusable.
Based on the present invention, it has been determined that a metal diaphragm, of the type used in an oil filled transducer, when increased in thickness renders a value where the diaphragm can exhibit and accommodate extremely large pressures and deflect to cause a lower pressure to be transmitted to the oil. Because of the large thickness of the metal diaphragm, the diaphragm will deflect, but a large amount of pressure is dissipated in the diaphragm, whereas a fraction of the applied pressure is transmitted to the oil and hence to the silicon sensors.